Digital lighting technologies, i.e. illumination based on semiconductor light sources, such as light-emitting diodes (LEDs), offer a viable alternative to traditional fluorescent, HID, and incandescent lamps. Functional advantages and benefits of LEDs include high energy conversion and optical efficiency, durability, lower operating costs, and many others. Recent advances in LED technology have provided efficient and robust full-spectrum lighting sources that enable a variety of lighting effects in many applications. Some of the fixtures embodying these sources feature a lighting module, including one or more LEDs capable of producing different colors, e.g. red, green, and blue, as well as a processor for independently controlling the output of the LEDs in order to generate a variety of colors and color-changing lighting effects.
It is desirable to extend the lifetime of LED light sources with an LED-based lighting unit. It may be particularly desirable to extend the lifetime of the LED-based lighting unit in certain installation locations and/or in certain installation scenarios, for example when installed in a difficult to reach area (e.g., a tunnel and/or in street lighting), to have a relatively long lifetime, to thereby lessen the frequency with which the LED-based lighting unit would need to be serviced and/or replaced.
To extend lifetime, some conventional LED-based lighting units utilize redundant LEDs that are activated if primary LEDs become inoperable. For example, current flowing to a primary LED may be shunted to a redundant LED upon failure of the primary LED. Such a technique requires complete failure of a primary LED prior to activation of the redundant LED and may present one or more drawbacks. For example, such a technique may result in uneven light output in an LED-based lighting unit between a newly activated redundant LED and a broken-in primary LED; may hasten the failure of the primary LED; and/or may result in more serious issues to the LED-based lighting unit upon failure of the primary LED.
To extend lifetime, some other conventional LED-based lighting units utilize a temperature sensor to sense an overheat situation that may be detrimental to the lifetime of one or more LEDs and switch off the one or more LEDs and/or reduce the light output of the one or more LEDs in response to the overheat situation. Such a technique may present one or more drawbacks such as requiring temperature sensors that may reduce reliability of the LED-based lighting unit and/or causing non-uniformly distributed light output in some situations.
To extend lifetime, yet other conventional LED-based lighting units switch between LEDs of the LED-based lighting unit based on a determined cumulative energized time of each of the LEDs to minimize the cumulative energized time of each of the LEDs. Such switching is done in a strictly predefined manner that requires a central controller and a control network between the LED nodes of the LED-based lighting unit. Such a technique may present one or more drawbacks such as necessitating a central controller be utilized, necessitating a control network between the LED nodes, and/or requiring that the switching be performed in a strictly predefined manner.
Thus, there is a need in the art to provide methods and apparatus that enable control of one or more properties of light output of one or more LEDs of an LED node of an LED-based lighting unit to extend the lifetime of the LED-based lighting unit and that may optionally overcome one or more drawbacks of existing techniques.